Los Angeles Chargers Joey Bosa sacks Denver Broncos quarterback Trevor Siemian in the second half at the StubHub Center in Carson, California on October 22, 2017. The Chargers won 21 to 0. Photo by Lori Shepler/UPI | License Photo

ENGLEWOOD, Colo. -- When the defense accounts for only 16.5 points and 1.5 touchdowns allowed per game in a four-game stretch -- and your team loses three of those games, all by double digits -- it's not difficult to see which pistons aren't firing.

The Denver Broncos' offense currently languishes in an uncomfortable, frustrating silence. Since it racked up eight touchdowns and 59 points in a 2-0 start, it has lumbered to just three touchdowns and 42 points in its last four games.

In Los Angeles, the offense collapsed entirely, enduring a 21-0 shutout, snapping the club's streak of 394 consecutive games in which it had managed to score. The last time the Broncos were shut out before Sunday, Tommy Maddox was the Broncos' fill-in quarterback, George Bush -- the first one -- was the president and the Broncos were in Los Angeles -- playing the Raiders, a few long passes up the 110 from the StubHub Center where they were blanked Sunday afternoon.

As bad as it was for Siemian, it could have been worse. Three potential interceptions were dropped. Only eight completions in his last eight attempts after the Broncos trailed by three scores saved his day from a complete statistical disaster.

But he was also under pressure from the start, harassed by Los Angeles' defensive line into a pair of fumbles -- one of which was lost -- and five sacks. He was pressured on roughly one-third of his dropbacks. The Chargers didn't have to sacrifice coverage to pressure him, either; on one play, the Broncos tried to capitalize off defensive end Melvin Ingram's edge aggression with a screen pass, but he read the play perfectly and single-handedly blew it up.

One day after the defeat, Broncos head coach Vance Joseph reaffirmed his commitment to Siemian.

After watching the film, Joseph laid the blame for the shutout on the offense at large.

"It's not what I've seen from Trevor, it's the entire unit," Joseph said. "No one's perfect. He can't play well if he's not being protected in certain spots. He hasn't been perfect either and he can play better absolutely, but it's not a Trevor problem. It's a unit problem."

And the unit isn't keeping him upright enough. It also isn't generating enough space for the running backs to operate the last two weeks, which has led to subsequent breakdowns.

But it also all comes back to turnovers. Siemian lost one fumble and threw an interception, and tight end A.J. Derby fumbled on the third play of the game. This was the second consecutive game in which the Broncos have turned over the football three times, and their minus-8 turnover margin for the season is their worst after six games since 1982.

That strike-shortened season saw the Broncos finish 2-7. They can only hope that a longer campaign offers a chance for improvement and a better result this time.

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Not only is the offense failing to avoid giveaways, the defense can't generate takeaways.

In a pattern that looks numbingly familiar to late last season, the Broncos are seeing opponents get the ball out quickly and rarely throw at cornerbacks Aqib Talib and Chris Harris Jr., instead opting for short passes to running backs and tight ends that limit the Broncos' chances for interceptions and strip-sack fumbles of opposing quarterbacks.

Denver's defense leads the league in total yardage allowed and is the only defense in the league that has not given up a rushing touchdown so far this season.

"Think about it, they don't throw the ball down the field, really. Most of the plays we've given them have been very great schemed-up plays that they're doing. They're scheming us, they're setting pick plays and they're figuring out ways to empty us out with three tight ends."

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The Broncos began devolving after Riley Dixon hit a low, line-drive punt that was returned 65 yards by Travis Benjamin for a touchdown that put the Chargers in front to stay.

Although there were coverage breakdowns on the play, the issues began with Dixon's punt, which Broncos head coach Vance Joseph described as "awful."

"It hit the ground and bounced right to (Benjamin)," Joseph said. "The plan was to put the ball to the sideline and kind of trap the guy because he has great speed. Once the punt's bad, the coverage ended up suffering because of the punt being so flat. Unacceptable. We can't do it."

It was part of a difficult day on special teams for the Broncos, with poor decisions and bad bounces that led to them starting five drives after kickoffs and punts from inside the 20-yard line, including three from inside their 10.

NOTES: WR Emmanuel Sanders walked without crutches and a boot through the locker room Monday, eight days after spraining his ankle against the Giants. Sanders is considered "day-to-day." ... WR Cody Latimer is expected to return to practice this week after missing three games because of a knee injury. ... OLB Shane Ray is expected to make his regular-season debut next Monday against the Chiefs. Ray has been on injured reserve all season because of torn wrist ligaments suffered on the first day of training camp. ... RT Menelik Watson is considered "day-to-day" after sitting out the Chargers game because of a calf injury, Broncos head coach Vance Joseph said. ... RT Donald Stephenson did not play after suffering a calf injury in practice last Thursday. He is considered "week-to-week," Broncos head coach Vance Joseph said. ... QB Paxton Lynch accompanied the team to Los Angeles as he continues to take throwing sessions in his recovery from a sprained right shoulder. Lynch has not practiced since he was injured Aug. 26. ... WR Isaiah McKenzie is "day-to-day" because of a sprained ankle, Broncos head coach Vance Joseph told KDSP-AM 760 in Denver on Monday. McKenzie missed the Chargers game after suffering the injury against the Giants on Oct. 15. ... ILB Todd Davis is being evaluated after suffering a high ankle sprain Sunday. Davis was seen in a walking boot Monday while moving through the locker room.

REPORT CARD VS. CHARGERS

--PASSING OFFENSE: D-minus - Forty pass plays resulted in three turnovers, five sacks and no points. The turnovers included a pair of fumbles -- one by quarterback Trevor Siemian as he tried to elude edge rusher Chris McCain, and another by tight end A.J. Derby on the third play of the game after he caught a 23-yard pass from Siemian near the left sideline. Siemian got into a groove late; he completed his final eight passes, but by then the game was decided.

--RUSHING OFFENSE: D - For a second consecutive week, the Broncos couldn't mount any consistent push against a struggling run defense as the Chargers limited them to just 69 yards on 19 carries. C.J. Anderson's 11-yard run in the third quarter was Denver's longest of the day, as the well of explosive runs into which the Broncos tapped so frequently in Weeks 1-4 seems to have dried up against defenses that are clogging the box more often.

--PASS DEFENSE: B - Until being burned by a game-clinching 42-yard catch-and-run by Travis Benjamin, the Broncos kept Philip Rivers and the Chargers' passing game largely in check, particularly on third downs. Still, the Broncos find themselves in the situation they were in last year -- playing from behind, without enough offensive firepower to force opposing teams to attack them downfield, effectively taking Chris Harris Jr. and Aqib Talib out of the equation. As a result, the Giants and Chargers have barely tested the Broncos downfield, and neither All-Pro cornerback has an interception since Week 2.

--RUSH DEFENSE: B - Once again, the Broncos bottled up Chargers running back Melvin Gordon, holding him to just 38 yards on 18 carries -- 21 of which came on a single run. A goal-line stand early in the first quarter saw the Broncos stuff Gordon on four consecutive runs from the 1-yard line. Without that stand, the game would have gotten out of hand long before it did.

--SPECIAL TEAMS: F - New coordinator Brock Olivo's enthusiasm hasn't translated into solid performances from the special teams, and their work bottomed out in Los Angeles. The troubles began when fill-in kickoff returner Brendan Langley made an ill-advised decision to return the opening kickoff from three yards deep in his end zone; he got caught out of position and was eventually stopped at the Denver 9-yard line. But what sealed the failure of the day was allowing Travis Benjamin to race 65 yards for a touchdown on a punt return, a play set up by what head coach Vance Joseph called an "awful" Riley Dixon punt, a low line-drive shot that didn't allow the Broncos' coverage unit a chance to get downfield. Langley had a 61-yard kickoff return in garbage time and Hunter Sharp filled in ably for Isaiah McKenzie on punt returns, but these were of little consolation given that Dixon's punt led to a backbreaking return that was all the scoring the Chargers needed.

--COACHING: C-minus - Head coach Vance Joseph said after the game that the team's practices went well -- just like he did last week. Something is getting lost in the translation and the execution. The Broncos started slowly for a second consecutive week; this time it was special teams that let them down early. Denver couldn't find another gear at halftime and the result was the Broncos' first shutout in nearly a quarter-century.